One aspect relates to an apparatus comprising a ceramic body having a tunnel and a tunnel filling, comprising a first constituent and a second constituent, wherein the electrical conductivity of the first constituent and of the second constituent differs by at least 5·104 S/m; a further apparatus, especially a precursor of the preceding apparatus, especially a green body; a method, especially for producing an electrical feedthrough or a green body of an electrical feedthrough; a ceramic precursor, especially a green body, obtainable by the aforesaid method; a further apparatus, especially an electrical feedthrough, obtainable by the aforesaid method; an electrical device, especially an implantable electrical medical device; a use of an aforesaid apparatus; a use of the aforesaid ceramic precursor; a method comprising implanting the aforesaid implantable electrical medical device; and a use of the aforesaid implantable electrical medical device.
Disclosed in the prior art are numerous implantable electrical medical devices, as for example pacemakers, defibrillators and electrocardiographs (ECG devices). The known pacemakers include bladder pacemakers, respiratory pacemakers, intestinal pacemakers, diaphragmatic pacemakers, cerebral pacemakers and, for example, cardiac pacemakers. Such devices are typically implanted into a human animal organism in order to therapeutize, treat or monitor a disease or dysfunction of the organism. For this purpose there must always be an electrical connection between the device interior and the surroundings of the device housing. For instance, a pacemaker when deployed is intended to generate an electrical voltage pulse in the interior of the pacemaker housing by way of an electrical pulse generator, and to deliver this pulse via an electrode outside the pacemaker housing to organic tissue of the patient. An implanted measuring device such as an ECG device or biomonitor records electrical voltage signals via measuring electrodes outside the device housing, and passes them into the housing for processing. In each case it is necessary to provide an electrical connection, often a multiplicity of electrical connections, between the interior and the surroundings of the housing. At the same time, however, it must be ensured that the housing interior is hermetically closed off from the organic surroundings. In the prior art, this is done using electrical feedthroughs. A prior-art electrical feedthrough includes an electrically conducting feedthrough element, typically a platinum wire or a pin, which extends from the device interior to the outside. The feedthrough element here is insulated electrically from the housing, which typically consists of a titanium alloy, typically by means of a ceramic ring. The required hermetic sealing of the feedthrough is typically achieved by welding a titanium flange into an opening of the housing and soldering or welding the ceramic ring into this flange. The feedthrough element is soldered into the ceramic ring with a gold solder. In order to achieve hermetic sealing, accordingly, numerous connections between different components and materials are produced in the prior art, using expensive materials such as the gold solder. This leads to very complicated and expensive production methods and also to disadvantages with regard to the reliability of the device. The various connection sites are potential sites of breakage and leakage. Leakage of an implanted electrical medical device, however, must be avoided at all costs. If such a device develops leakages, it may harm the patient, or the device fails and is no longer able to fulfil its function. This is particularly serious in view of the diseases to be treated by a pacemaker, such as heart conditions, for example. Even if defects in the device are recognized promptly, the replacement of the device implies a considerable surgical intervention into the patient's body.
In this connection, cermet feedthroughs exhibit considerable advantages. They are produced by introducing a feedthrough channel in a green ceramic compact with a cermet paste and firing the two together. Accordingly, the ceramic insulating body and the electrically conducting feedthrough element are produced in one piece without inter-material connections. In order to achieve a suitable density of the cermet feedthrough element, a suitable thermal expansion behaviour and effective bonding to the ceramic body, it is advantageous to use a cermet having not too a high metal fraction, typically a fraction of platinum. In order then for the cermet feedthrough element to be able to be utilized as such, it must be contacted electrically at both ends, in the housing interior and on the side facing the patient body, by means of soldering, bonding or welding. For successful such electrical connection, a surface with an increased metal fraction and/or an increased electrical conductivity is needed on the feedthrough element. In the prior art, such a surface is applied subsequently, additionally, to the feedthrough element, by means, for example, of the printing of a paste and subsequent firing or sintering, by means of thermal spraying, or by means of thin-film coating. In each case, additional method steps on each side of the feedthrough element produce at least one additional inter-material connection. This, however, runs exactly counter to the fundamental concept of a one-piece cermet feedthrough. The production process for the prior-art cermet feedthrough therefore becomes more complicated and more expensive. Furthermore, the additional connection points render the prior-art feedthrough less mechanically robust and durable.
For these and other reasons, a need exists for the present embodiments.